This invention relates to a method for the production of an anhydrous powdered dextrose which contains large amounts of anhydrous .beta.-dextrose from aqueous dextrose solutions or from aqueous solutions containing dextrose.
It is known that there are three types of crystals in dextrose, anhydrous .alpha.-dextrose crystals, monohydrate .alpha.-dextrose crystals and anhydrous .beta.-dextrose crystals. Of these, the anhydrous .beta.-dextrose has the advantages of having a more rapid rate of dissolution, better solubility in cold water and showing less caking phenomenon during dissolution compared to the monohydrate and anhydrous .alpha.-dextroses. The anhydrous .beta.-dextrose also has the further advantage over the monohydrate dextrose that it can be utilized to avoid the problem of moisture content, whereas the monohydrate dextrose has a moisture content of about 9% in the form of crystalline water.
To date, the crystallization methods used for dextrose have been classified as the boiling method, whereby crystals are formed under the condition of a moderate degree of supersaturation and the crystals are centrifugally separated from the formed massecuite, and the total sugar method, whereby separation is not done and the total solid fraction is taken from the sugar solution as the product.
The boiling method yields a highly pure product, but due to the immense investment in equipment, the low yield, the long time required, etc., the production costs are quite large. On the other hand, in the total sugar method, the caking and grinding process, the spray-drying process, etc., must be carried out. This encounters problems in the caking and grinding process such as a long time being required for the caking operation, and the powder becomes sticky during the grinding operation and adheres to the mill, etc. Furthermore, although various spray-drying processes exist, they generally have the problems of requiring large amounts of dry seed crystals, curing equipment for after the spraying, etc. Also, in the total sugar method, there has been difficult to treate the free water during the crystallization.
Regarding the production of anhydrous .beta.-dextrose, processes utilizing the boiling method have been known; for example, Japanese Patent Specification No. SHO 46-25690, but no processes based on the total sugar method have yet been available for the simple and easy production of anhydrous powdered dextrose containing large amounts of anhydrous .beta.-dextrose.
The prior art processes also include Japanese Patent Specification No. SHO 37(1962)-30377 which discloses a sugar crystallization process wherein a sugar solution heated through a long pipe is spouted into a vacuum evaporator and then air is blown into the sugar concentrate which has about 9% water content and is sedimented on the bottom of the evaporator, thereby crystallizing the concentrate by convection; and Japanese Patent Specification No. SHO 36(1961)-25250 which discloses a process for the production of crystalline dextrose wherein a dextrose solution is concentrated to a point where the water content is less than 9%, and then the concentrate is introduced into a closed vessel with an agitator and strongly agitated to form crystals by mixing the concentrate with air.